1. Field of the Invention
The present invention relates to a driver for moving a movable member by driving a drive shaft with which the movable member is frictionally engaged by using a piezo element or the like controlled to expand and contract at different speeds, and a control method for the driver. More particularly, the present invention relates to a reproducing apparatus for reproducing information by drivably moving a head by driving a drive shaft with which the head is frictionally engaged by using a piezo element or the like controlled to expand and contract at different speeds, a head transfer apparatus, and a head transfer method.
2. Description of the Related Art
Hitherto, there has been known a method using the combination of a rotating motor, a rack and a pinion gear to move a read-write head in a radial direction. The read-write head is adapted to record data in a recording medium, such as a disk, and reproduce the data from the recording medium. The head fixed to the rack moves as the pinion gear fixed to the rotating shaft of a motor rotates as the motor revolves, and the rack meshed with the pinion gear moves as the pinion gear rotates.
The head driving method based on the combination of the rack, the pinion gear and the rotating motor has been disadvantageous in that it is difficult to reduce the size of the motor for obtaining an adequate motor torque for driving the pinion gear.
To solve the problem, a head transfer mechanism using an impact drive actuator has been proposed. The head transfer mechanism has an oscillating element, such as a piezo element, a drive shaft secured to one end of the piezo element, and a head frictionally engaged with the drive shaft or a frictional engagement member to which a head is secured.
This type of driver using the aforesaid conventional impact drive actuator will be described in conjunction with FIG. 1 showing the construction of the driver.
Reference numeral 1 denotes a piezo element serving as an oscillating element formed of a piezoelectric ceramic constituent, which is the impact drive actuator. A rod 2 is firmly secured by an adhesive agent or the like to one end, namely, the right end, the piezo element 1 oscillating in the right direction. A counterbalance 3 is firmly secured by an adhesive agent or the like to the other end of the piezo element 1. The counterbalance 3 is retained by a support member 4 supported by a chassis, which is not shown. The other end of the rod 2 is held by the support member 4 such that no play occurs in the shaft diameter direction, while an allowance for oscillation is provided in the axial direction.
Reference numeral 5 denotes a driven member, e.g., an optical pickup. The optical pickup 5 receives the lower surface of the rod 2 by a frictional connection surface 6 on the upper side in the drawing. The upper surface of the rod 2 is in frictional contact with a leaf spring 7, as shown in FIG. 3. This means that the optical pickup 5 frictionally holds the rod 2 between the frictional connection surface 6 and the leaf spring 7.
The optical pickup 5 has a guide shaft 8 parallel to the rod 2 and supported mainly by the chassis 9. Guide bearings 10, 10 of the optical pickup 5 are held by the guide shaft 8. Thus, the optical pickup 5 is movable in the radial direction of a disk, not shown, that is held by chucking of a spindle motor 11.
The impact drive actuator is driven by applying a square-wave voltage (FIG. 2) to the piezo element 1 to cause oscillation or the expansion and contraction to take place, thereby moving the optical pickup 5. More specifically, when the piezo element 1 slowly expands, as indicated by a waveform S1, the optical pickup 5 in frictional contact with the rod 2 moves. When the piezo element 1 instantaneously contracts, as indicated by a waveform S0, the optical pickup 5 slides and stops. This expansion and contraction is repeated to drive the optical pickup 5.
In the impact drive actuator, however, the force of friction between the rod 2 and the optical pickup 5 may change if, for example, wastes or dust stick to the rod 2 or the inertial force of the optical pickup 5 causes a frictional contact surface 6 to excessively press the rod 2. To prevent such a change, increasing the drive voltage applied to the piezo element 1 is being considered. However, in the case of a battery-driven apparatus, the voltage cannot be increased due to a restricted battery voltage. Therefore, applying a higher voltage may not be ideal corrective measures to prevent the changes in the frictional force described above.